Co-channel wireless communication methods and systems using relayed wireless communications

ABSTRACT

Wireless communications are transmitted from at least two radioterminals to a base station co-channel over a return link using a return link alphabet. Wireless communications are also transmitted from the base station to the at least two radioterminals over a forward link using a forward link alphabet that has more symbols than the return link alphabet. The co-channel signals are deciphered at the receiver, while the radioterminals can use a smaller return link alphabet, which can reduce the power dissipation at the radioterminals.

CROSS-REFERENCE TO RELATED APPLICATION

This application is continuation of U.S. patent application Ser. No.12/021,515, entitled Co-Channel Wireless Communication Methods andSystems Using Relayed Wireless Communications, filed Jan. 29, 2008 nowU.S. Pat. No. 7,831,201 which a divisional of and claims priority toU.S. patent application Ser. No. 10/795,875, entitled Co-ChannelWireless Communication Methods And Systems Using NonsymmetricalAlphabets, filed on Mar. 8, 2004 now U.S. Pat. No. 7,444,170 and claimsthe benefit of Provisional Application Ser. No. 60/457,043, entitledSatellite Assisted Push-To-Send Radiotelephone Systems and Methods,filed Mar. 24, 2003; Provisional Application Ser. No. 60/457,118,entitled Radio Frequency Communication Systems and Methods That UsePolarization Orthogonality to Double Channel Capacity, filed Mar. 24,2003; Provisional Application Ser. No. 60/473,959, entitled Systems andMethods That Enable Co-Channel Communications With a Base Station of aPlurality of Radioterminals, filed May 28, 2003; and ProvisionalApplication Ser. No. 60/477,522, entitled Satellite AssistedPush-To-Send Radioterminal Systems, Methods and Protocols, filed Jun.11, 2003, all of which are assigned to the assignee of the presentinvention, the disclosures of all of which are hereby incorporatedherein by reference in their entirety as if set forth fully herein.

FIELD OF THE INVENTION

This invention relates to wireless communications methods and systems,and more particularly to wireless communication systems and methods thatcan communicate co-channel.

BACKGROUND OF THE INVENTION

Polarization diversity receiving systems and methods are well known inwireless communications. For example, a wireless terminal may transmit alinearly-polarized signal that may be received by orthogonally polarizedantennas (e.g., horizontal and vertical polarization) at a base station(terrestrial or space-based) to thereby separately receive orthogonallypolarized portions of the transmitted signal. The orthogonally polarizedportions may be combined to effectively increase link robustness, sincemany channel degradations such as fading, are largely uncorrelated whencomparing antennas of orthogonal polarizations. See for example, U.S.Pat. No. 6,526,278 to Hanson et al. entitled Mobile SatelliteCommunication System Utilizing Polarization Diversity Combining; U.S.Pat. No. 5,724,666 to Dent entitled Polarization Diversity Phased ArrayCellular Base Station and Associated Methods; U.S. Pat. No. 6,418,316 toHildebrand et al. entitled Increasing Channel Capacity of Wireless LocalLoop via Polarization Diversity Antenna Distribution Scheme; and U.S.Pat. No. 6,445,926 to Boch et al. entitled Use of SectorizedPolarization Diversity as a Means of Increasing Capacity in CellularWireless Systems.

Other systems and methods that use polarization effects in wirelesscommunications are described in the following publications: Andrews etal., Tripling the Capacity of Wireless Communications UsingElectromagnetic Polarization, Nature, Vol. 409, Jan. 18, 2001, pp.316-318; Wolniansky et al., V-BLAST An Architecture for Realizing VeryHigh Data Rates Over the Rich-Scattering Wireless Channel, Invitedpaper, Proc. ISSSE-98, Pisa, Italy, Sep. 29, 1998, pp. 295-300; andCusani et al., A Simple Polarization-Recovery Algorithm forDual-Polarized Cellular Mobile-Radio Systems in Time-Variant FadedEnvironments, IEEE Transactions in Vehicular Technology, Vol. 49, No. 1,January 2000, pp. 220-228.

It is also known to use diversity concepts to increase the capacity ofwireless communications. See, for example, the following publications:Miller et al., Estimation of Co-Channel Signals With Linear Complexity,IEEE Transactions on Communications, Vol. 49, No. 11, November 2001, pp.1997-2005; and Wong et al., Performance Enhancement of Multiuser MIMOWireless Communications Systems, IEEE Transactions on Communications,Vol. 50, No. 12, December 2002, pp. 1960-1970.

SUMMARY OF THE INVENTION

Some embodiments of the present invention transmit wirelesscommunications from at least two radioterminals to a base stationco-channel over a return link using a return link alphabet, and transmitwireless communications from the base station to the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet. As used herein, the term“co-channel” indicates signals that overlap in time and space, and thatuse the same carrier frequency, the same time slot if the signals areTime Division Multiple Access (TDMA) signals, and the same spreadingcode if the signals are Code Division Multiple Access (CDMA) signals,such that the two signals collide at a receiver. Embodiments of thepresent invention can allow the co-channel signals to be decoded ordeciphered at the receiver, and can allow the radioterminals to use asmaller return link alphabet which can reduce the power dissipation atthe radioterminals.

In some embodiments of the present invention, the wirelesscommunications are transmitted from the base station to theradioterminals non-co-channel over the forward link using the forwardlink alphabet that has more symbols than the return link alphabet. Inyet other embodiments, co-channel transmissions may be used. In someembodiments, wireless communications are transmitted from the at leasttwo radioterminals to at least one antenna at the base stationco-channel over a return link using a return link alphabet. In otherembodiments, these transmissions are made to at least onemultiple-polarized antenna at the base station. In yet otherembodiments, these transmissions are made to a plurality ofmultiple-polarized antennas at the base station. In still otherembodiments, these transmissions are made to a plurality ofmultiple-polarized antennas in a single sector of the base station. Insome embodiments, the wireless communications are transmitted to theplurality of multiple-polarized antennas in a sector if the at least tworadioterminals are separated by more than a predetermined distance. Inother embodiments, these transmissions are made to at least onemultiple-polarized antenna in at least two sectors of the base station.In yet other embodiments, these transmissions are made to at least onemultiple-polarized antenna at a first base station and at least onemultiple-polarized antenna at a second base station. In still otherembodiments, these transmissions are made from a singlelinearly-polarized antenna at each of the at least two radioterminals.

Other embodiments of the present invention transmit wirelesscommunications from at least two radioterminals to a base station over areturn link using a return alphabet and transmit wireless communicationsfrom the base station to the at least two radioterminals co-channel overa forward link using a forward link alphabet that has more symbols thanthe return link alphabet. In other embodiments, as was described above,the transmission from the radioterminals to the base station may benon-co-channel or co-channel. Moreover, the wireless communications maybe transmitted from the base station to at least one antenna at each ofthe at least two radioterminals, to at least one multiple-polarizedantenna at each of the at least two radioterminals and/or to a pluralityof multiple-polarized antennas at each of the at least tworadioterminals, co-channel over a forward link using a forward linkalphabet that has more symbols than the return link alphabet, as wasdescribed above. Transmission from the base station may use at least oneantenna, at least one linearly-polarized antenna, at least twolinearly-polarized antennas, at least two linearly-polarized antennas ina sector, at least one linearly-polarized antenna in at least twosectors and/or at least one linearly-polarized antenna at two or morebase stations, as was described above.

In other embodiments of the present invention, wireless communicationsare received from a base station at a first radioterminal and at leastone second radioterminal that is proximate the first radioterminal overa forward link, co-channel. The wireless communications are relayed fromthe at least one second radioterminal to the first radioterminal over ashort-range wireless link. The wireless communications that are relayedto the first radioterminal from the at least one second radioterminalover the short-range wireless link are used to process the wirelesscommunications that are received from the base station at the firstradioterminal. Moreover, these embodiments may be combined with any ofthe embodiments that were described above.

Still other embodiments of the present invention bidirectionallytransmit wireless communications co-channel in time division duplex fromat least two radioterminals to a base station over a return link using areturn link alphabet, and from the base station to the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet. These embodiments alsomay be combined with any of the embodiments that were described above.

It will be understood by those having skill in the art that embodimentsof the present invention were described above primarily with respect tomethod aspects. However, other embodiments of the present inventionprovide systems, base stations and radioterminals according to any ofthe embodiments that were described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 and 4A-4B are diagrams of co-channel wireless communicationsaccording to various embodiments of the present invention.

FIG. 5A is a diagram of radioterminal to base station communicationsaccording to embodiments of the present invention.

FIG. 5B is a diagram of base station to radioterminal communicationsaccording to embodiments of the present invention.

FIG. 5C is a diagram of base station to radioterminal communicationsaccording to other embodiments of the present invention.

FIGS. 6A-6B are block diagrams of receivers that may be used in FIGS.5A-5C according to embodiments of the present invention.

FIG. 7 graphically illustrates simulated receiver performance forsignals in Rayleigh fading channels according to some embodiments of thepresent invention.

FIG. 8 is a diagram of base station to radioterminal bidirectionalcommunications according to embodiments of the present invention.

FIG. 9 is a block diagram of a receiver and transmitter that may be usedin embodiments of FIG. 8.

FIG. 10 is a block diagram of a receiver that may be used in FIG. 9according to embodiments of the present invention.

FIG. 11 is a block diagram of a transmitter that may be used in FIG. 9according to embodiments of the present invention.

FIGS. 12 and 13 are diagrams of radioterminals and base stations,respectively, according to embodiments of the present invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Some embodiments of the present invention may arise from a recognitionthat it is possible to configure two physically distinct radioterminalsto transmit to a base station, also referred to as a base transceiverstation (BTS), co-channel, using the same return-link radio-channelresource(s) while still being able, at the BTS, to reliably demodulateand reconstruct (i.e., decode) the two data streams of the twophysically distinct radioterminals. It is also possible to configure aBTS to transmit to two physically distinct radioterminals co-channel,over the same forward-link radio-channel resource(s), while each of thetwo distinct radioterminals is able to reliably demodulate andreconstruct the information intended for it. The two physically distinctradioterminals may thus communicate bi-directionally with a BTS,co-channel, in some embodiments, using no more channel resource(s) thana single radioterminal would use. The signal processing techniques thatmake this possible, according to some embodiments of the invention, canexploit the multipath scattering nature of the radiochannel and/or themulti-dimensional nature of space and its relationship toelectro-magnetic wave propagation. Moreover, embodiments of theinvention can be extended to allow three or more physically distinctradioterminals to communicate co-channel with a BTS without using anymore radiochannel resource(s) than a single radioterminal would.

Some embodiments of the present invention may also arise from arecognition that co-channel communications may be more beneficial for aninfrastructure (base station) receiver than for a radioterminalreceiver, because an infrastructure transmitter may not be power limitedand may thus resort to a higher-alphabet modulation format (i.e. 8-PSK,16-QAM, 64-QAM, etc.) to increase channel capacity on a forward link. Incontrast, a radioterminal's transmitter may be power limited and maythus be constrained to lower-alphabet modulation formats (i.e. QPSK,GMSK, etc.). Thus, the ability of two or more radioterminals to sendinformation to an infrastructure element (base station) co-channel maybe used advantageously to increase channel capacity on the returnlink(s). According to some embodiments, therefore, base stations andradioterminals may be configured to utilize different modulationalphabets on forward and return links with a return link alphabet havinga smaller number of distinct states (symbols) than a forward linkalphabet, and with at least some infrastructure (base station) receiversof the system configured for co-channel communications, as will bedescribed in further detail below.

FIG. 1 is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to some embodiments of the presentinvention. As shown in FIG. 1, wireless communications are transmittedfrom at least two radioterminals 110 a and 110 b to a base station (BTS)120 co-channel over a return link 130 using a return link alphabethaving return link symbols S_(R). As also shown in FIG. 1, wirelesscommunications are transmitted from the base station 120 to the at leasttwo radioterminals 110 a and 110 b over a forward link 140 using aforward link alphabet having forward link symbols S_(F), wherein theforward link alphabet has more symbols than the return link alphabet. Inother words, S_(F)>S_(R). In some embodiments, the wirelesscommunications are transmitted from the base station 120 to the at leasttwo radioterminals 110 a and 110 b non-co-channel over the forward link140 using the forward link alphabet that has more symbols S_(F) than thereturn link alphabet S_(R).

Still referring to FIG. 1, the wireless communications are transmittedfrom the at least two radioterminals 110 a and 110 b to at least oneantenna 122 at the base station 120 co-channel over the return link 130using the return link alphabet. In some embodiments, the at least oneantenna 122 is at least one multiple-polarized antenna. In otherembodiments, the at least one antenna 122 is a plurality ofmultiple-polarized antennas.

In still other embodiments, the base station 120 includes a plurality ofsectors using sectorization techniques that are well known to thosehaving skill in the art. In some embodiments, the at least one antenna122 comprises a plurality of multiple-polarized antennas in a singlesector of the base station, such that wireless communications aretransmitted from the at least two radioterminals 110 a and 110 b to theplurality of multiple-polarized antennas in the single sector of thebase station 120 co-channel over the return link 130 using the returnlink alphabet. In other embodiments, the wireless communications fromthe at least two radioterminals 110 a and 110 b are transmitted to aplurality of multiple-polarized antennas 122 in the sector of the basestation 120 co-channel over the return link 130 using the return linkalphabet if the at least two radioterminals are separated by more than apredetermined distance D. In still other embodiments, the wirelesscommunications are transmitted from the at least two radioterminals 110a and 110 b to at least one multiple-polarized antenna 122 in at leasttwo sectors of the base station 120 co-channel over a return link usingthe return link alphabet.

FIG. 2 is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to other embodiments of the presentinvention. As shown in FIG. 2, the base station 120 is a first basestation. Wireless communications are transmitted from at least tworadioterminals 110 a and 110 b to at least one multiple-polarizedantenna 122 at the first base station and at least onemultiple-polarized antenna 222 at a second base station 220 co-channelover a return link 130 using a return link alphabet. In any of theembodiments of FIGS. 1 and/or 2, wireless communications may betransmitted from a single linearly-polarized antenna 112 a, 112 b ateach of the at least two radioterminals 110 a, 110 b to the base station120, 220 co-channel over the return link 130 using the return linkalphabet.

Accordingly, some embodiments of FIGS. 1 and 2 allow co-channeltransmissions from radioterminals to a base station using a smallelement alphabet in conjunction with non-co-channel transmissions fromthe base station to the radioterminals using a larger element alphabet.The number of antenna elements at the base station may be operativewithin a given sector of a base station, distributed over more than onesector of a base station and/or distributed over a plurality of basestations. As such, intra-sector co-channel return link communicationsmay be provided, as well as inter-sector and inter-base station returnlink co-channel communications, to provide potentially improved capacitycharacteristics. Moreover, in some embodiments, intra-sector co-channelcommunications between two or more radioterminals and a base station mayonly be allowed in response to a distance D between the radioterminals.Since the system can know the position of the radioterminals, based on,for example, GPS or other techniques, radioterminals that are, forexample, D meters or more apart may be allocated co-channel resources.Otherwise, non-co-channel resources may be allocated. The distance D maybe selected so as to provide sufficient multipath differentiation fromthe signals that originate from the two radioterminals that aretransmitting co-channel.

FIG. 3 is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to still other embodiments of thepresent invention. As shown in FIG. 3, wireless communications aretransmitted from at least two radioterminals 310 a, 310 b to a basestation 320 over a return link 330 using a return link alphabet havingreturn link symbols S_(R). Wireless communications are also transmittedfrom the base station 320 to the at least two radioterminals 310 a, 310b co-channel over a forward link 340 using a forward link alphabethaving forward link symbols S_(F), wherein the forward link alphabet hasmore symbols than the return link alphabet. In other words, S_(F)>S_(R).

Embodiments of FIG. 3 may be employed where it is desirable to relaymuch more data to the radioterminals 310 a, 310 b from the base station320 than to the base station 320 from the radioterminals 310 a, 310 b.This may be the case when the radioterminals may be receiving largefiles from the base station, whereas the radioterminals are only sendingback mouse clicks and/or other small amounts of data. Embodiments ofFIG. 3 use a larger element alphabet in conjunction with co-channelcommunications to serve two or more terminals, while the radioterminalsuse a smaller element alphabet and may communicate non-co-channel withthe system. In other embodiments, wireless communications aretransmitted from the at least two radioterminals 310 a, 310 b to thebase station 320 co-channel over the return link 330 using the returnlink alphabet.

Still referring to FIG. 3, in some embodiments, the wirelesscommunications are transmitted from the base station 320 to at least oneantenna 312 a, 312 b at each of the at least two radioterminalsco-channel over the forward link using the forward link alphabet thathas more symbols than the return link alphabet. In some embodiments, theat least one antenna 312 a, 312 b comprises at least onemultiple-polarized antenna. In other embodiments, the at least oneantenna 312 a, 312 b comprises a plurality of multiple-polarizedantennas. In other embodiments, the at least one antenna 322 at the basestation 320 comprises at least one linearly-polarized antenna, at leasttwo linearly-polarized antennas, at least two linearly-polarizedantennas in a single sector and/or a linearly-polarized antenna in atleast two sectors, as was described above in connection with theantennas 122 of FIG. 1. In still other embodiments, transmissions mayoccur to at least one linearly-polarized antenna at a first base stationand at a second base station, as was described above in connection withFIG. 2.

FIG. 4A is a diagram of co-channel wireless communications according toyet other embodiments of the present invention. As shown in FIG. 4A,wireless communications are received from a base station 420 at a firstradioterminal 410 a and at least one second radioterminal 410 b that isproximate the first radioterminal 410 a, over a forward link 440,co-channel. The wireless communications from the at least one secondradioterminal 410 b are relayed to the first radioterminal 410 a over ashort-range wireless link 450. The short-range wireless link may bebased on Bluetooth and/or other technologies such as 802.11, UWB, etc.The first radioterminal 410 a uses the wireless communications that arerelayed to the first radioterminal 410 a from the at least one secondradioterminal 410 b over the short-range wireless link 450, to processthe wireless communications that are received from a base station 420 atthe first radioterminal 410 a over the forward link 440.

Accordingly, in embodiments of FIG. 4A, the signals from one or moreproximate radioterminals may be used to improve a quality measure suchas a bit error rate, of the information that is being received from thebase station 420. It will also be understood by those having skill inthe art that embodiments of FIG. 4 need not use a forward link alphabetthat has more symbols than a return link alphabet. However, in otherembodiments of the invention, embodiments of FIG. 4 may be used with anyof the embodiments of FIGS. 1-3, including the use of a forward linkalphabet that has more symbols than a return link alphabet, co-channelcommunications from the radioterminals 410 a, 410 b to the base station420, and antenna configurations for the base station 422 and for theradioterminal antennas 412 a, 412 b similar to those described inconnection with FIGS. 1-3.

FIG. 4B is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to still other embodiments of thepresent invention. Referring to FIG. 4B, wireless communications arebi-directionally transmitted co-channel in Time Division Duplex (TDD)450. Time division duplex transmission is well known to those havingskill in the art, and need not be described further herein. As shown inFIG. 4B, bidirectional transmission co-channel in time division duplexproceeds from at least two radioterminals 460 a, 460 b to a base station470 over a return link using a return link alphabet, and from the basestation 470 to the at least two radioterminals 460 a, 460 b over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet. The antennas 462 a, 462 b of the first andsecond radioterminals 460 a, 460 b may be configured as was described inFIGS. 1-4A above. Moreover, the antenna or antennas 472 of the basestation 470 may be embodied as was described above in any of FIGS. 1-4A.

Additional discussion of co-channel wireless communications according tovarious embodiments of the invention now will be provided. Specifically,in accordance with “non-Time Division Duplex” (non-TDD) embodiments, thereceiver of a radioterminal and the receiver of a BTS may be configuredto operate on a plurality of signals that may be acquired via aplurality of spatially-separated and/or co-located antennas. Thetransmitter of a radioterminal may use a single antenna. The BTS maytransmit the information that is intended for a first radioterminal froma first antenna and the information that is intended for a secondradioterminal from a second antenna that may be spatially-separated fromthe first. The two radioterminals may use the same return-link channelresource(s) to transmit information to the BTS. The BTS may use the sameforward-link channel resource(s) to transmit information to the tworadioterminals. FIGS. 5A and 5B illustrate antenna configurations ofnon-TDD embodiments. It will also be understood that some embodiments ofFIGS. 5A and 5B may be used in TDD mode as well.

Those skilled in the art will recognize that the M dual-polarized (orcross polarized) receiver antennas 512 of a radioterminal 510, asillustrated in FIG. 5B, may be replaced by M triple (x, y, z)-polarized,linearly-polarized, circularly-polarized and/or other type of receiverantennas. In some embodiments, only some of the M dual-polarizedreceiver antennas 512 of a radioterminal 510, as illustrated in FIG. 5B,may be replaced with triple-polarized, linearly-polarized,circularly-polarized, and/or other type of antennas, and that the valueof M may be different for different radioterminals. In still otherembodiments, only one receiver antenna that has been tapped at differentpoints may be used on a radioterminal to provide a plurality of signalinputs to the radioterminal's receiver. It will also be understood bythose of skill in the art that the N dual-polarized receiver antennas540 of a BTS, as illustrated in FIG. 5A, may be replaced in part or inentirety by triple (x, y, z)-polarized, linearly-polarized,circularly-polarized, and/or other type of receiver antennas. Finally,those having skill in the art will also recognize that one or both ofthe linearly-polarized transmitter antennas 520 of a BTS, as illustratedin FIG. 5B, may be replaced by a dual- or multi-dimensionally-polarized,circularly-polarized and/or other type of transmitter antenna(s) andthat the linearly-polarized transmitter antenna 532 of a radioterminal530 may be replaced by a dual-polarized, multi-dimensionally-polarized,circularly-polarized and/or other type of transmitter antenna.

Those having skill in the art will also recognize that embodiments ofFIGS. 5A and 5B may be extended to accommodate L co-channelradioterminals (L>2) by having L transmitter antennas 520 on the BTSwith the λ^(th) such antenna (λ=1, 2, . . . , L) transmittinginformation intended for a corresponding λ^(th) radioterminal.

Referring now to FIG. 5C, in environments of dense radioterminalcommunications, such as in airports, convention centers, shopping malls,etc., one or more radioterminals 550 b-550 n that is/are proximate to afirst co-channel radioterminal 550 a may be configured to providesignals to the first receiving co-channel radioterminal 550 a. Thesesignals may be relayed from the one or more proximate radioterminals 550b-550 n to the first receiving co-channel radioterminal 550 a viashort-range wireless links 552. The first receiving co-channelradioterminal 550 a may be configured to process the signals receivedfrom the one or more proximate radioterminals so as to improve a qualitymeasure, such as the Bit Error Rate (BER), of the information that isbeing received from the BTS. Still referring to FIG. 5C, one or moreradioterminals 550 b′-550 n′ that is/are proximate to a secondco-channel radioterminal 550 a′, may be configured to provide signals tothe second receiving co-channel radioterminal 550 a′. These signals maybe relayed from the one or more proximate radioterminals 550 b′-550 n′to the second receiving co-channel radioterminal 550 a′ via short rangewireless links 552. The second receiving co-channel radioterminal 550 a′may be configured to process the signals received from the one or moreproximate radioterminals, so as to improve a quality measure such as theBER of the information that is being received from the BTS. Accordingly,two or more radioterminals such as radioterminals 550 a and 550 a′ mayoperate co-channel. It also will be understood that some embodiments ofFIG. 5C may be used in TDD mode as well.

A linear receiver processor, in accordance with the well-known LeastMean Squared Error (LMSE) criterion, is illustrated in FIG. 6A fornon-TDD embodiments. Those skilled in the art will recognize that otherlinear and/or non-linear receiver processors such as, for example,Kalman-based, least squares, recursive least squares, Zero Forcing (ZF)and/or Maximum Likelihood Sequence Estimation (MLSE) etc, may be used inlieu of and/or in combination with the receiver processor of FIG. 6A. Italso will be understood that FIG. 6A illustrates a receiver for a BTS,but the principles and architecture may also be applied to aradioterminal.

In accordance with the illustrative BTS receiver antenna array 540 ofFIG. 5A, each antenna of the array 540 operates in two spatialdimensions and provides two signals to the receiver: one correspondingto the first spatial dimension “vertically-polarized” and the othercorresponding to the second spatial dimension “horizontally-polarized.”Thus, in accordance with the receiver antenna array that is illustratedin FIG. 5A, the i^(th) antenna (i=1, 2, . . . , N) provides the receiverwith the signal inputs V_(i) and H_(i). As is illustrated in FIG. 6A,each signal of the set {V₁, H₁, V₂, H₂, . . . , V_(N), H_(N)} isoperated on by two transversal filters 610 a, 610 b; one for eachco-channel source (radioterminal). The transversal filter outputs aresummed at 620 a, 620 b, to produce an output signal S′j (j=1, 2) basedon which a decision is made at Blocks 630 a, 630 b regarding theinformation symbol that has been transmitted by the j^(th) co-channelsource. The transversal filters may be fractionally spaced,synchronously spaced, or single tap filters.

A computer simulation has been developed to assess the potentialefficacy of the receiver of FIG. 6A. FIG. 7 graphically illustratesresults of the computer simulation. The simulation modeled twoco-channel radioterminals each transmitting independent data usingBinary Phase Shift Keyed (BPSK) modulation with no Forward ErrorCorrection (FEC) coding. The computer simulation modeled burstytransmission to emulate GSM. Within each burst of data, the channel wasassumed static and an a priori known to the receiver training sequence(the burst mid-amble in GSM terminology) was used to estimate thetransversal filter coefficients of the receiver. For each burst of dataa new Rayleigh fading channel was picked pseudo-randomly. FlatRayleigh-fading channels were assumed. Consequently, there was noInter-Symbol Interference (ISI), only non-dispersive Co-channelInterference (CCI) due to the co-channel radioterminal. Thus, thereceiver transversal filters reduced to single coefficient devices. TheBit Error Rate (BER) was evaluated for several receiver antennaconfigurations as described below.

As shown in FIG. 7, for the case of four dual-polarized receiverantennas, the uncoded Rayleigh-faded channel BER for each co-channelradioterminal, at E_(b)/N₀ of 4 dB, is ˜10⁻³, whereas the BER ofclassical BPSK in Additive White Gaussian Noise (AWGN) with no fading,at the same E_(b)/N₀ of 4 dB is ˜10⁻². Thus, the simulations appear toshow that not only has the receiver of FIG. 6A reduced the CCI, butsignificant diversity gain has also been attained.

To potentially improve further on the receiver performance of FIG. 6A, areceiver architecture of FIG. 6B may be used. The receiver of FIG. 6Buses an estimate of the co-channel signal that has minimum noise and/orinterference variance to cancel the CCI in the other co-channel signal,thus reducing or minimizing noise enhancement in the other co-channelsignal, since a regenerated noise-free estimate of the CCI may now beused in the cancellation. Referring again to FIG. 6A, the noise and/orinterference variance of the two co-channel decision variables S′_(i)and S′₂ may be estimated once per “data burst.” The duration of the databurst may be chosen small relative to the rate-of-change of the channelstate so as to validate a static (or quasi-static) channel assumptionover a given data burst. The estimate of noise and/or interferencevariance of S′_(j) (j=1, 2) may, for example, be based on the magnitudeof a linear superposition of squared transversal filter weights, thatmay be involved in forming S′_(j) or may be based on processing of an apriori known to the receiver, training sequence. In the illustrativeexample of FIG. 6B, the noise and/or interference variance of S′₁ hasbeen found to be smaller than the noise and/or interference variance ofthe second decision variable, S′₂. Thus, the decision that is made onS′₁, assumed correct, may be used to form an improved decision variableS″₂, based on which a decision or a series of decisions may be maderegarding the data elements transmitted by the second co-channelradioterminal.

It will be understood by those of skill in the art that, in theillustrative receiver processing of FIG. 6B, if the second decisionvariable was found to have lower noise and/or interference variance, adecision on that variable may have been made and that decision may havebeen used to form an improved first decision variable. It will also beunderstood by those skilled in the art that the principle and receiverarchitecture that is illustrated on FIG. 6B, of first deciding on theleast noise and/or interference variance variable and then using thatdecision to improve the noise and/or interference variance of the seconddecision variable, may be extended similarly to the general case wherethere are L co-channel radioterminals and, therefore, L decisionvariables at the receiver. In that case, the one (out of the L) decisionvariable with minimum noise and/or interference variance will beidentified, a decision on it will be made, and that decision will beused to improve the noise and/or interference variance of the secondleast noise and/or interference variance variable. Then, a decision onthe improved second least noise and/or interference variance variablewill be made and now both decisions that have been made thus far can beused to improve the decision variable of the third least noise and/orinterference variance variable, etc. Finally, it will be understood thateven though the receiver principles and architectures of FIGS. 6A and 6Bhave been described using nomenclature associated with a BTS, theprinciples and receiver architectures of FIGS. 6A and 6B, and variationsthereof, are also applicable to the radioterminal.

FIG. 8 illustrates two radioterminals communicating co-channelbidirectionally with a BTS in a TDD mode according to other embodimentsof the present invention. When the radioterminals 830 transmitinformation to the BTS antennas 840, a BTS receiver of FIGS. 6A and/or6B may be used to process the received waveforms, as was alreadydescribed, and make decisions on the data that has been transmittedco-channel to the BTS antennas 840 by the radioterminals 830. Thisfunction is illustrated by Block 910 of FIG. 9. The BTS receiver of FIG.9 may also be configured to perform processing of the received waveformsin accordance with the well-known zero-forcing criterion thereby“forcing to zero”, to the extent that digital quantization effectsand/or other implementation constraints may allow, the ISI and the CCI,at least over the span of the transversal filters used. This function isillustrated by Block 920 of FIG. 9 and is further illustrated in greaterdetail in FIG. 10.

Over the time interval of a TDD frame, the state of the channel may beassumed static or quasi-static provided that the TDD frame interval hasbeen chosen sufficiently small. Thus, capitalizing on the reciprocity ofthe TDD channel over its static or quasi-static interval the transversalfilter coefficients that have been derived by the BTS receiver to yield“zero” ISI and CCI at the BTS, may be used to process or pre-distort aBTS data vector d prior to transmitting it to the co-channelradioterminals. In TDD, the same BTS antenna array may be performingboth receive and transmit functions. This function is illustrated byBlock 930 of FIG. 9 and is further illustrated in greater detail in FIG.11. It also will be understood that some embodiments of FIG. 8 may beused in non-TDD mode, as well.

Given the above, the information that is transmitted by a BTS,co-channel, for a plurality of radioterminals, can arrive at theplurality of co-channel radioterminals free, or substantially free, ofISI and CCI. Thus, the receiver complexity of a radioterminal may bereduced and the radioterminal may only be equipped with a singlelinearly-polarized receiver antenna. Those skilled in the art willrecognize that even in TDD mode the principles and receiverarchitectures that were described earlier for the non-TDD case can applyfor both a BTS and a radioterminal. Also, those skilled in the art willrecognize that the zero-forcing processing at a BTS receiver asillustrated in FIGS. 9 and 10 may be omitted and instead, thetransversal filter coefficients derived from a LMSE processor (Block 910of FIG. 9) may be used for the transmitter processing (Block 930 of FIG.9) of a BTS. Accordingly, information that is received when wirelesslyreceiving at least two signals on the same carrier frequency, timeinterval, and/or code, from a corresponding at least two radioterminals,may be discriminated among the at least two signals.

Finally, it will be understood that, in all of the embodiments that havebeen described herein, a radioterminal may include a transceiver whichitself includes a transmitter and a receiver, as illustrated in FIG. 12,which perform the transmitting and receiving operations, respectively,that were described herein. The antenna of the radioterminal may beregarded as a component of the transceiver. Similarly, in all of theembodiments described herein, a base station may also include atransceiver which itself includes a transmitter and a receiver, asillustrated in FIG. 13, which perform the transmitting and receivingoperations, respectively, that were described herein. The antenna of thebase station may be regarded as a component of the transceiver.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1. A wireless communications method comprising: receiving first andsecond wireless co-channel communications, at each element, of aplurality of elements, of an antenna that is associated with a sector ofa base station, from respective first and second physically distinctradioterminals; and processing a respective plurality of signals, thatis provided by the plurality of elements of the antenna that isassociated with the sector of the base station, to recover data; whereinreceiving first and second wireless co-channel communications, at eachelement, of a plurality of elements, of an antenna that is associatedwith a sector of a base station, from respective first and secondphysically distinct radioterminals comprises: receiving first and secondsignals, from the respective first and second physically distinctradioterminals, at each element, of the plurality of elements, of theantenna that is associated with the sector of the base station; thefirst and second signals overlapping therebetween in time, space andfrequency; and, if the first and second signals that are received fromthe respective first and second physically distinct radioterminals, ateach element, of the plurality of elements, of the antenna that isassociated with the sector of the base station, relate to a CodeDivision Multiple Access (CDMA) protocol, receiving a first signal fromthe first radioterminal, at each element, of the plurality of elements,of the antenna that is associated with the sector of the base station;the first signal from the first radioterminal having been spread by aspreading code; and receiving a second signal from the secondradioterminal, at each element, of the plurality of elements, of theantenna that is associated with the sector of the base station; thesecond signal from the second radioterminal having been spread by thesame spreading code as the first signal from the first radioterminal. 2.The method according to claim 1, further comprising: transmittingnon-co-channel wireless communications from the base station to thefirst and second radioterminals.
 3. The method according to claim 1,further comprising: transmitting co-channel wireless communications fromthe base station to the first and second radioterminals.
 4. The methodaccording to claim 3, wherein transmitting co-channel wirelesscommunications from the base station comprises: transmitting first andsecond wireless communications signals from respective first and secondantennas; wherein the first and second wireless communications signalsoverlap in time, space and frequency; and use the same spreading code ifthe signals relate to a Code Division Multiple Access (CDMA) protocol.5. The method according to claim 1, wherein the antenna that isassociated with the sector of the base station comprises at least onemultiple-polarized antenna and/or a plurality of antennas that arespaced apart therebetween.
 6. The method according to claim 5, whereinthe at least one multiple-polarized antenna comprises a plurality ofmultiple-polarized antennas.
 7. The method according to claim 1, whereinthe base station comprises a plurality of sectors and wherein eachsector of the plurality of sectors comprises an antenna that includes aplurality of antenna elements.
 8. The method according to claim 7,further comprising: receiving the first and second wireless co-channelcommunications using first and second antennas in respective first andsecond sectors of the base station.
 9. The method according to claim 1,wherein the base station is a first base station and wherein receivingfirst and second wireless co-channel communications comprises: receivingwireless communications using at least one antenna at the first basestation and using at least one antenna at a second base station.
 10. Themethod according to claim 1, wherein receiving first and second wirelessco-channel communications further comprises: receiving first and secondwireless co-channel communications responsive to a distance between thefirst and second radioterminals exceeding a predetermined threshold andreceiving first and second wireless communications that are notco-channel from the first and second radioterminals responsive to thedistance between the two radioterminals being less than, or equal to,the predetermined threshold.
 11. The method according to claim 1,wherein processing a respective plurality of signals that is provided bythe plurality of elements of the antenna that is associated with thesector of the base station, to recover data, comprises: processing therespective plurality of signals to derive first data that is associatedwith a first one of the first and second physically distinctradioterminals; and using the first data to derive second data that isassociated with a second one of the first and second physically distinctradioterminals.
 12. A base station comprising: a receiver that isconfigured to receive first and second wireless co-channelcommunications, at each element, of a plurality of elements, of anantenna that is associated with a sector of the base station, fromrespective first and second physically distinct and separateradioterminals and to process a respective plurality of signals, that isprovided by the plurality of elements of the antenna that is associatedwith the sector of the base station, to recover data; wherein the firstand second wireless co-channel communications that are received at eachelement, of the plurality of elements, of the antenna that is associatedwith the sector of the base station, from the respective first andsecond physically distinct and separate radioterminals are overlappingtherebetween in time, space and frequency; and wherein if the first andsecond signals that are received from the respective first and secondphysically distinct and separate radioterminals, at each element, of theplurality of elements, of the antenna that is associated with the sectorof the base station, relate to a Code Division Multiple Access (CDMA)protocol, the first signal from the first radioterminal, that isreceived at each element, of the plurality of elements, of the antennathat is associated with the sector of the base station comprises a firstspreading code and the second signal from the second radioterminal thatis received at each element, of the plurality of elements, of theantenna that is associated with the sector of the base station comprisesa second spreading code that is the same as the first spreading code.13. The base station according to claim 12, further comprising: atransmitter that is configured to transmit wireless communications tothe first and second radioterminals that are not co-channeltherebetween.
 14. The base station according to claim 12, furthercomprising: a transmitter that is configured to transmit wirelesscommunications to the first and second radioterminals that areco-channel therebetween.
 15. The base station according to claim 14,wherein the transmitter is configured to transmit first and secondwireless communications signals, from respective first and secondantennas, such that the first and second wireless communications signalsoverlap in time, space and frequency and use the same spreading code ifthe first and second wireless communications signals relate to a CodeDivision Multiple Access (CDMA) protocol.
 16. The base station accordingto claim 12, wherein the antenna that is associated with the sector ofthe base station comprises at least one multiple-polarized antennaand/or a plurality of antennas that are spaced apart therebetween. 17.The base station according to claim 16, wherein the at least onemultiple-polarized antenna comprises a plurality of multiple-polarizedantennas.
 18. The base station according to claim 12, wherein the basestation comprises a plurality of sectors and wherein each sector of theplurality of sectors comprises an antenna that includes a plurality ofantenna elements.
 19. The base station according to claim 18, whereinthe receiver is further configured to receive the first and secondwireless co-channel communications using first and second antennas inrespective first and second sectors of the base station.
 20. The basestation according to claim 12, wherein the base station is a first basestation and wherein the receiver is further configured to receive thefirst and second wireless co-channel communications by receivingwireless communications using at least one antenna at the first basestation and using at least one antenna at a second base station.
 21. Thebase station according to claim 12, wherein the receiver is furtherconfigured to receive first and second wireless communications, from therespective first and second physically distinct and separateradioterminals, that are co-channel therebetween, responsive to aseparation distance between the first and second radioterminalsexceeding a predetermined threshold and to receive first and secondwireless communications, from the respective first and second physicallydistinct and separate radioterminals, that are not co-channeltherebetween, responsive to the separation distance between the firstand second radioterminals being less than, or equal to, thepredetermined threshold.
 22. The method according to claim 12, whereinthe receiver is further configured to process the respective pluralityof signals to derive first data that is associated with a first one ofthe first and second physically distinct and separate radioterminals andto use the first data to derive second data that is associated with asecond one of the first and second physically distinct and separateradioterminals.
 23. A radioterminal comprising: a transmitter that isconfigured to transmit wireless communications to a base station; and areceiver that is configured to receive first and second signals that areco-channel therebetween, to process the first and second signals toderive first data that is associated with information that istransmitted by the base station to a device other than the radioterminaland to use the first data to derive second data that is associated withinformation that is transmitted by the base station to theradioterminal.
 24. The radioterminal according to claim 23, wherein thereceiver is further configured to form first and second decisionvariables, to associate with each one of the first and second decisionvariables a measure of noise and/or interference, to select one of thefirst and second decision variables responsive to a noise and/orinterference content thereof, to make a first decision based upon theselected decision variable and to use the first decision to make asecond decision; wherein the first and second decision variablescorrespond to respective first and second information that istransmitted co-channel by the base station, the first decision comprisesdata that is transmitted by the base station and is intended for thedevice other than the radioterminal and the second decision comprisesdata that is transmitted by the base station and is intended for theradioterminal.
 25. The radioterminal according to claim 23, wherein thereceiver is configured to receive the first and second signals using atleast one antenna.
 26. The radioterminal according to claim 25, whereinthe at least one antenna comprises at least one multiple-polarizedantenna and/or a plurality of antennas that are spaced aparttherebetween.
 27. The radioterminal according to claim 26, wherein theat least one multiple-polarized antenna comprises a plurality ofmultiple-polarized antennas.
 28. The radioterminal according to claim23, wherein the receiver is further configured to decode at least one ofthe first and second signals.
 29. The radioterminal according to claim23, wherein the first and second signals overlap in time, space andfrequency and use the same spreading code if the first and secondsignals relate to a Code Division Multiple Access (CDMA) protocol.
 30. Aradioterminal comprising: a receiver that is configured to receivewireless communications from a base station, to receive wirelesscommunications from at least one second radioterminal and to use thewireless communications that are received from the at least one secondradioterminal to process the wireless communications that are receivedfrom the base station.
 31. The radioterminal according to claim 30:wherein the receiver is configured to receive wireless communicationsfrom the base station over a forward link using a forward link alphabet;and wherein the radioterminal further comprises a transmitter that isconfigured to transmit wireless communications to the base station usinga return link alphabet that has fewer symbols than the forward linkalphabet.
 32. The radioterminal according to claim 30, wherein thereceiver is further configured to process the wireless communicationsthat are received from the base station and the wireless communicationsthat are received from the at least one second radioterminal to derivefirst data that is not intended for the radioterminal and to use thefirst data to derive second data that is intended for the radioterminal.